The major objective of the Harvard Medical School Research Center in Diagnostic Radiology is to examine, understand, improve and amplify the varied elements of medical imaging. The specific goal of the Center is the enhancement of imaging information yield by physical, chemical and pharmacologic means. This will be accomplished by collaboration among scientists from disciplines which range among all subspecialities of Radiology through those involved in perceptual psychology; the physics of Radiology, Computed Tomography and Ultrasound; Physiology, Pharmacology, Nuclear Medicine, Radiopharmaceutical Chemistry, Engineering, Computer Science, Electronics and Decision Analysis. The Center investigators will work to improve ultrasonic imaging by Digital Processing and by evaluating the ultrasonic properties of tissues; to improve radionuclide imaging both with new devices and new imaging agents; to assess the information yield of densitometric analysis versus conventional radiographic methods; to evaluate perceptual factors determining image information yield; to enhance image yield by pharmacologic methods; and to analyze the threshold sensitivity of radiographic techniques. Because there are many combined basic laboratory and clinical research projects underway; a particular objective of the Center is the rapid transfer of advances made in the laboratory to the clinical setting. Furthermore, the multifaceted approaches to problems permit a comparison of competing imaging modalities both as to information yield and "biologic" (radiation) cost. In developing its research potential, the Center also serves as a training resource for investigators and academic radiologists both from Harvard and other Medical Schools.